456 CERVICAL NERVES. 



The Spinal nerves are divided into 



Cervical .... 8 pairs 



Dorsal . . . . 12 

 Lumbar .... 5 



Sacral .... 6 



The cervical nerves pass off transversely from the spinal cord ; the 

 dorsal are oblique in their direction ; and the lumbar and sacral verti- 

 cal ; the latter form the large assemblage of nerves at the termination 

 of the cord called cauda equina. 



CERVICAL NERVES. 



The cervical nerves increase in size from above downwards ; the 

 first (sub-occipital) passes out of the spinal canal between the occipital 

 bone and the atlas ; and the last, between the last cervical and first 

 dorsal vertebra. Each nerve, at its escape from the intervertebral 

 foramen, divides into an anterior and a posterior branch. The anterior 

 branches of the four upper cervical nerves form the cervical plexus; the 

 posterior branches, the posterior cervical plexus. The anterior branches 

 of the four inferior cervical together with the first dorsal form the 

 brachial plexus. 



ANTERIOR CERVICAL NERVES. The anterior branch of the first 

 cervical nerve escapes from the vertebral canal through the groove upon 

 the posterior arch of the atlas which supports the vertebral artery, be- 

 neath which it lies. It then descends in front of the transverse pro- 

 cess of the atlas, sends several twigs to the rectus lateralis and recti 

 antici, and forms an anastomotic loop by communicating with an 

 ascending branch of the second nerve. 



The anterior branch of the second cervical nerve at its exit from 

 the intervertebral foramen between the atlas and the axis, gives twigs 

 to the rectus anticus major, scalenus posticus and levator anguli 

 scapulae muscles and divides into three branches, viz. an ascending 

 branch, which completes the arch of communication with the first 

 nerve ; and two descending branches, which communicate with the 

 third nerve. 



The anterior branch of the third cervical nerve, double the size of 

 the preceding, divides at its exit from the intervertebral foramen into 

 numerous branches, some of which are distributed to the rectus major, 

 longus colli, and scalenus posticus muscles, while others communicate 

 and form loops and anastomoses with the second and fourth nerve. 



The anterior branch of the fourth cervical nerve, of the same size 

 with the preceding, sends twigs to the rectus major, longus colli, 

 and levator anguli scapulae, communicates by anastomosis with the 

 third, and sends a small branch downwards to the fifth nerve. Its 

 principal branches pass downwards and outwards across the posterior 

 triangle of the neck, towards the clavicle and acromion. 



